Is there any technical document explaining the details of "sa" account including the permissions, the roles that are assigned to "sa" account.
You shouldn't use the sa account in SQL server. The recommendation is to lock down the sa account. See the following link on how you can do that:
I like the comments from the authors of NGSSQLCrack they "are relatively certain that they can brute force any SQL Server password under 8 or 9 characters in 15 hours or less"
I am not sure if there is anything specifically written around the sa account, a fair starting place would be to search for "security" or "sa account" on Books OnLine (press F1 from SSMS), there you will get details of best practices for using the sa account and how to secure your server.
Our policy here is to set the sa password to something very long and complex and then (hopefully) never use the account for anything (not in scheduled jobs, DTS/SSIS packages, stored procedures, etc). The password is recorded just in case we ever have to use the sa account to recover a server after a crash.
Use the minimum security possible that allows the process in consideration to execute successfully.
The sa account can do anything on the server, it is the first account to be created when SQL is installed.
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